The present invention relates in general to improvements in epicyclic transmissions and more particularly to improvements for providing stable transmission operation over a wide operating range.
Modern rotating machinery is required to operate at high speeds. The definition of high speed operation is, of course, related to the size of the machinery; however gas turbine speeds over 50,000 rpm are not uncommon. Therefore, devices transferring power from such high speed machinery must themselves be capable of high-speed operation. Such devices are frequently called upon to perform a concomitant function of reducing a high-speed input to a low-speed output. It is desirable that this speed reduction be accomplished in as few steps as possible since the amount of equipment required to accomplish the total speed reduction depends upon the number of steps required. Therefore, it is advantageous for a power transmission device to be capable of providing both stable high-speed operation and large speed reduction ratios.
As in any rotating machinery, problems accompanying unreacted (uncompensated) centrifugal forces, unsynchronized operation or inefficient operation are inherent in power transmissions. These problems are obviously intensified when such devices are operated at high-speeds. The undesirable effects of these problems are legion: vibration; noise; and unreliability being but a few. Furthermore, at high speeds any instability in operation is at best inefficient, and at worst disastrous.
Large speed reduction requirements tend to worsen the above-described problems. Speed reduction ratios in the order of 100 to 1 are desirable. In addition to reducing the amount of necessary equipment, large speed reduction ratios provide versatility to a transmission. By having a large speed-reduction ratio, the transmission can be applied to a wide variety of machinery and speeds of operation. The resulting cost savings are obvious.
One form of power transmitting device often used in high-speed applications is an epicyclic transmission. Epicyclic transmissions are susceptible to problems similar to those inherent in the above discussed power transmitting devices. Examples of attempts to improve the performance of epicyclic transmissions are Braren, U.S. Pat. No. 1,867,492 and Gorfin, U.S. Pat. No. 3,258,994. The devices discussed in these patents purport to improve transmission performance by providing various configurations for the transmission gearing. However, these devices are not addressed to problems associated with unreacted centrifugal forces arising in the transmission rotating members. Therefore these devices are susceptable to unstable operation at high speeds.
Kari, U.S. Pat. No. 3,324,746 is an example of an epicyclic transmission having means for counterbalancing only some of the centrifugal forces developed therein. The Kari device has an eccentric ring or a balanced wheel to counter centrifugal forces developed in the driving shaft. The centrifugal forces result from eccentric segments positioned on the driver shaft. The ring or wheel is mounted on the driver shaft, but at a position diametrically opposed (180.degree.) to the eccentric segments also positioned on the shaft. The Kari device therefore serves only to counterbalance centrigual force developed in the driver shaft. During high-speed operation, if is desirable to counter all centrifugal forces which are developed in any of the rotating members. Any unbalanced forces, as above-discussed, can become dangerous.
The present invention overcomes the above-discussed problems by counteracting and reducing essentially all centrifugal forces developed in an epicyclic transmission.
In the preferred transmission embodiments of the invention, transfer of torque to the output shaft is accomplished without the use of gears. By eliminating gears, problems attendant therewith are also eliminated. Such problems may include those resulting from vibration and noise. In high torque applications, gear failure is a very real problem. Therefore, transmission reliability is also improved by eliminating gears.